Re: How to replace the interstage transformer with tube PI?


"RS" <RS@xxxxxxxxxx> wrote in message
news:0gkni457p5lqpdvdqo1utrvmkpiagi58os@xxxxxxxxxx
On Tue, 25 Nov 2008 02:43:21 -0600, "Stephen Cowell"
<scowell@xxxxxxxxxxxxx> wrote:


"RS" <RS@xxxxxxxxxx> wrote
...
I'd say the best way to go would be to make an incandescent
roach from a Fender neon one... just cut it open, put in an
equivalent lamp (24v?) and heat-shrink the thing together.

What kind of problems have you encountered with CdS cells? "On"
resistance? "Off" resistance? Linearity?

Speed... you go too fast, they don't track closely
enough. Speed-dependant depth is not good... but
it's in the nature of the beast... CdS is slow. It takes
a really good cell to get a decent tremolo.

The VTL5C1 should be fast enough, right? 35ms turn-off.
http://www.aikenamps.com/VTL5C1.pdf
http://optoelectronics.perkinelmer.com/content/datasheets/dts_vtl5c1c2.pdf

There are even faster ones, but I don't remember seeing these in MI
apps. Maybe too expensive:
http://optoelectronics.perkinelmer.com/content/datasheets/dts_vtl5c9c10.pdf

Probably a balance to be struck... engineering fun! Call
and ask for samples, say you're with Nunya, Inc.

The Fender I'm talking about is the old one... heat-shrinked.
The Vactec devices I'm familiar with are plastic-encased.

Not sure if the older ones are still in production. Perkin Elmer
bought both Vactec and Reticon (mfg of the bucket brigade delays used
in original flangers and choruses). The P-E search engine has
problems--I couldn't locate the single-component CdS's, but they may
be still available.

http://optoelectronics.perkinelmer.com/search/search.aspx?Ntt=cadmium+sulfide&NavSearchButton.x=0&NavSearchButton.y=0
(most of the links don't work)

Look up... see Hubble? Remember problems? Think P-E.

I agree about making your own roach. That's not difficult. I'd check
into LEDs though. Should be able to light one up with the same
circuit, with current limit resistor. Might need a paralleled
resistor to put the driver's voltage/current in range, but that
shouldn't be tough either.

LEDs give a sharper envelope, perhaps desirable with
the more sluggish cheeseball cells available at RatShak.

If you're looking for tighter response time, wouldn't you want that?
The incancescents (like old Magnatones) were slow due to the filament
lag. Some like the rolloff from incandescent/CdS because it rounds
off the trem depth as speed is turned up--avoids choppy sound.

This is part of the UniVibe magic... incandescents give
a sinusoidal wave output from a choppy input.

I don't remember ever using tremolo on anything except Harlem
Nocturne, but I use CdS's in other stuff. Chorus/Flanging and
switching.

Spy music... yum! TMBG uses tremolo to good effect.
Tremolo, reverb, and Leslie is heaven.

Opto trem sucks anyway... it always has that speed
dependant depth thing going on. Bias trem does it
for me... or that brownface hi-lo trem is cool.

Many like some of the old Fender circuits cause they had that 'pseudo
chorus' thing going on. Probably what you're referring to as hi-lo.

Stare at the schematic for about an hour... it's a hi-lo thing.

I like CdS cells in general. Nice to have free-floating isolated
resistors.

They're not kind to your signal... should not be used as pass
elements. When you depend on them, they'll fail... they drift,
very temperature sensitive. One of the first places to look in
a failing amp with lots of knobs and footswitches.
__
Steve
..


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